1. Field of the Invention
The present invention relates generally to the art of removing flash from workpieces which have been molded from such flexible materials as rubber, plastics, and the like. More particularly, the present invention relates to a closed recirculation cryogen shot blast deflashing apparatus which, in its preferred form, (1) moves workpieces to be deflashed about in a treatment chamber, (2) exposes the workpieces in the treatment chamber to a high velocity flow of cryogen gas (preferably nitrogen) to rapidly embrittle workpiece flash, (3) impacts workpieces in the treatment chamber with particulate media which is projected from a throwing wheel to remove embrittled flash from the workpieces, (4) recirculates cryogen gas and particulate media from and to the treatment chamber in a highly efficient manner, (5) utilizes a recirculating flow of pressurized cryogen gas to act as a carrier for particulate media being delivered to the throwing wheel, and (6) employs a purging system for introducing an inert gas such as nitrogen into the closed recirculation system of the deflashing apparatus to purge the apparatus of ambient air before cryogen introduction is begun, and to maintain a positive pressure inert atmosphere throughout the apparatus to inhibit entry of moisture laden ambient air and thereby prevent condensation of moisture and the formation of ice inside the apparatus.
2. Prior Art
When articles are molded from flexible materials such as rubber, plastics and the like, the resulting articles often have thin pieces of unwanted flexible material extending therefrom called "flash" which must be removed to conform the articles to their desired final configurations. Removing flash from articles formed from flexible materials is difficult in view of the soft, elastic nature of the flexible materials. While various types of mechanical trimming operations have been proposed for use in extricating unwanted flash, these proposals have proven not to be economically feasible in a majority of applications.
In order to simplify and reduce the cost of flash removal, proposals of various types have been made for "freezing" or otherwise cooling molded articles to embrittle their thin sections of flash, whereafter one or a combination of mechanical processes have been utilized to break off, trim or otherwise remove the "frozen" or embrittled flash.
The use of cryogen materials such as liquid nitrogen to effect embrittlement of workpiece flash is known. As utilized herein, the term "cryogen" will be understood to refer broadly to substances which are fluids and are at temperatures of about -60.degree. F. and below.
The use of shot blast deflashing machinery in single and plural stage processes to remove cryogen-embrittled flash is known. Previous proposals for cryogen shot blast deflashing apparatus have been characterized by a number of drawbacks. Proposed apparatus typically have been of complex and expensive construction, and have exhibited less than the desired degree of reliability. Such systems as have been proposed for (1) withdrawing particulates including media and pieces of flash from treatment chambers, (2) segregating reusable media, and (3) returning the reusable media to throwing wheels have not functioned entirely satisfactorily. A problem quite common to apparatus embodying previous proposals is that ambient air which contains moisture is able to enter the system, whereupon in the cold cryogen environment of the system, the moisture condenses and forms ice that results in clogged and/or "frozen" flow lines and valves.
In short, most previously proposed cryogen shot blast deflashing apparatus have been quite costly to build, costly to maintain, and costly to operate; moreover, their operation has been undependable in that it has been characterized by undesirably frequent and lengthy intervals of machine "down time."
3. The Referenced Applications
The invention of the referenced Apparatus Case addresses the foregoing and other drawbacks of previously proposed cryogen deflashing systems, and provides a novel and improved cryogen deflashing system which is greatly simplified in construction and arrangement, and which operates with significantly improved efficiency. While the referenced Apparatus Case notes the need to maintain a cryogen atmosphere throughout the closed system of the apparatus to prevent entry of moisture laden ambient air and to prevent moisture condensation and ice formation, the Apparatus Case does not specifically call for the provision of an inert gas purging system that utilizes a gas such as nitrogen to purge the system of ambient air prior to the introduction of cryogen, and to maintain a positive pressure inert atmosphere throughout the apparatus to inhibit entry of moisture laden ambient air and thereby prevent condensation of moisture and the formation of ice. The present invention addresses this need by providing such a purging system, with the purging system including significant features that have been developed and proven through experimentation.
The referenced Bellows Return Conduit Case and the referenced Jointed Supply Conduit Case relate to recirculation and supply conduit features that are utilized in the deflashing system of the referenced Apparatus Case. The features that form the subject matter of these applications are described and illustrated in the parent Apparatus Case, and are likewise described and illustrated herein for completeness and to satisfy the "best mode" description requirement of the patent law.